To adapt the steering wheel position to the seating position of the driver of a motor vehicle, steering columns in various embodiments are known in the prior art. In addition to height adjustment by adjustment of the slope of the steering column, it is possible in steering columns to position the steering wheel attached to the rear end of the steering spindle in the interior of the vehicle by length adjustment in the direction of the steering column longitudinal axis.
The ability for length adjustment is achieved by virtue of the fact that the adjusting unit, which comprises the steering spindle rotatably mounted in a casing tube, can be adjusted telescopically in the longitudinal direction relative to the holding or carrier unit, which provides a steering column holder connected in a fixed manner to the vehicle body, and can be fixed in different longitudinal positions by means of a releasable clamping device, i.e. can be fixed releasably. The clamping device, also referred to as a fixing device, acts on the adjusting unit held by the holding unit, wherein movement of the adjusting unit relative to the holding unit in the longitudinal direction to adjust the steering wheel position is possible in the open state of the clamping device—also referred to as the unlocked position or release position—and, in the closed state—referred to as the fixing position or locking position—the adjusting unit is clamped to the holding unit and, in normal driving mode, the steering wheel position is fixed under the mechanical loads to be expected.
One known effective measure for improving occupant safety in a vehicle collision, the “event of a crash” or frontal impact of the vehicle, in which the driver strikes the steering wheel at high speed, is to make the steering column collapsible in the longitudinal direction, even in the fixing position of the clamping device, if a high force exceeding a limit which only occurs in the event of a crash is exerted on the steering wheel. In order to ensure controlled braking of a body striking the steering wheel, an energy absorption device is coupled between the holding unit and the adjusting unit, which are clamped and fixed to one another by the clamping device in the normal mode, as described, but are pushed together relative to one another in the event of a crash. This converts the kinetic energy introduced into plastic deformation of an energy absorption element, e.g. by tearing a tear tab or bending an elongate bending element, e.g. a bending wire or bending strip, or by expanding a slotted hole by means of a bolt or by stretching a sheet-metal strip or severing a burr by means of a plane.
A steering column of the type in question is described in DE 10 2008 060 225 A1. The clamping device described therein comprises a clamping mechanism having an actuating element designed as a clamping spindle. A rotary movement of the clamping spindle exerted via an operating lever is converted by the clamping mechanism into a clamping stroke, which exerts a force on the holding unit in the transverse direction, with the result that the adjusting device mounted therein is firmly clamped in a manner comparable to the operation of a clamp. Nonpositive fixing of the adjusting unit in the longitudinal direction is thereby achieved.
In the case of the abovementioned construction of a steering column, the activation of the energy absorption device (crash device) is accomplished by means of the clamping device during the fixing of the adjusting unit. Here, a fastening section of the energy absorption element (crash element), e.g. a bending strip, connected to the adjusting unit, is passed in the longitudinal direction through a through opening in a wedging lever or wedging housing, which, for its part, is supported in the longitudinal direction on the holding element. In particular, for crash activation, during the actuation of the actuating element, i.e. during turning of the clamping spindle, a force is exerted on the wedging housing by the actuating element in the fixing position, with the result that the wedging housing is turned about an axis perpendicular to the longitudinal axis and to the clamping spindle. The fastening section of the energy absorption element is thereby tilted in the through opening, with the result that, when a force acts in the longitudinal direction, the oblique edge regions of the inner wall are pressed transversely to the longitudinal direction against the surface of the energy absorption element and clamp it. Owing to the frictional forces which arise, the energy absorption element is fixed in the longitudinal direction in the wedging housing, similarly to the adjustable clamping arm on the rail of a C-clamp. The compact construction and the possibility of fixing the steering column position in an infinitely variable manner in the longitudinal direction is advantageous with this type of activation of the crash device.
Crash activation upon actuation of the clamping device offers considerable gain in terms of safety for the vehicle occupants. However, the disadvantage in the prior art is that damage to the edges of the energy absorption element in the form of notches can arise each time locking is carried out by tilting within the through opening, as a result of which the energy absorption behavior and hence crash rating can be impaired. Moreover, adjustment of the steering column can be made more difficult by catching of the damaged edges.
Thus a need exists for a steering column that has improved crash activation, with which the energy absorption behavior and adjustability are not negatively affected, even by repeated locking.